Method of making acoustic diaphragms



y 1952 J. B. BRENNAN 2,596,645

METHOD OF MAKING ACOUSTIC DIAPHRAGMS Filed Jan. 10, 1947 2 SHEETSSHEET l y 13, 5 J. B. BRENNAN 2,596,645

I METHOD OF MAKING ACOUSTIC DIAPHRAGMS v Filed Jan. 10, 1947 I 2 SHEETSSHEET 2 YIIIII/I/II 27 Patented May 13, 1952 METHOD OF MAKING ACOUSTIC "DIAPHRAGMS Joseph B Brennan, Cleveland, Ohio Applicatio njanuary 10, 1947, Serial No. 721,315

Qleime- 2- This invention relates to methods oi'making acoustic di'aphragms and particularly to the making of fibrous diaphragms 'ofithe. type used in loudspeakers and the like. i

In myparent application Serial No. 365,916 tiled November 12, 1940, now matured into Ratent No. 2,302,178, there is disclosed andclaimed a diaphragm having circumferentiallyv spaced weakened areas adjacent its periphery to in: crease the flexibility of the supporting part of the diaphragm. The present invention relates specifically to methods of producing diaphragms of this type and'theipresent application is a continuation'in part'of my application Serial No. 39,142 filedNovember-lz, 19410, now. abandoned, whichis in turn a division of said application SerialNo. 365,916.

One of theobjects ofathe invention is to .provide a method of making acoustic diaphragms in which circumferentially spaced areas adjacent the periphery of the diaphragm are formed with less strength than the adjacent, areas.

Anotherrobject is to'provide a method oimake ing diaphragms in which. less fibrous materialis deposited at circumferentially 'sPa'cedareasadjacen't-the peripherythan in adjacent areas. The invention contemplates several specifically different stepsito produce this effect including reducing the amount of fibrous material sprayed onto a format such areas or reducing the vac.- uum to which such areasja're subjected urin deposition of fibrous material.

Still. another object. is to provide a method of formingdiaphragms which taper in thickness from the 'centralportion toward the periphery. In a preferred method this is accomplished by depositing fibrous material from a suspension at a uniform level onto. a concave form.

The. above and. other objects and advantages of the invention will be more readily apparent from the following description when read in connection with the accompanying drawings, in

which- Figure 1 is a face view of a diaphragm formed according to the present invention;

' Figure'Z is a transverse section;

Figure 3 i' s'aj partial sectiono'n'the line a s of Figure'2;

Figure 4 is a view similar to Figure-3 of analternative construct-ion;

Figure 5 is a diagrammatic sectional view of one form of apparatus for making-'diaphragms;

Figure 6 is a partial section similar to Fig ure 5 of an alternative apparatus; i

Figure 7 is a diagrammatic top view oistill another form of apparatus;

Figure 8 is a partial enlarged section on the lined-8 of Figure'Z;

Figure 9 is a diagrammatic view otan apparatus for forming. diaphragms'a'ccording' to an al-J 'eri tive m t q V l l l pigu're'w is a part l section on-the line 19- 4 E 2, of Figure 9 illustrating the blocking members; Figure -11 i s a view similar to Figure 9 of an alternative form of apparatus;

Figure 12 is a view similar to Figure 9 illustrating the condition ofthe apparatus at the end of a depositing operation; and

Figure 13 is a partial perspective view of an alternative diaphragm structure.

Figures l to 3 illustrate a diaphragm like that described and claimed in my Patent No. 2,302,178 of the generally conical type provided at its smaller end with a cylindrical neck portion to which a moving voice coil may besecured. The diaphragm, as shown, is integrally formed of fibrous material with a generally conicalbody portion l6 adapted to vibrate in response to movements of the voice coil and which has integral therewith a rim or flange portion H. The rim or flange l l is generally flat and may, if desired, be formed with one or more circumferential corrugations 2 to increase its flexibility The diaphragm is supported through the rim or flange which may be clamped or otherwise secured to a support such as a speaker frame. It will be understood that the fibrous material from which the diaphragm is formed may be compressed to increase its density following the depositing opsimilar materials. Impregnation may be accornplished by mixing the impregnatin g materi al with the fibers prior to deposition or by adding the impregnating materials to the deposited fibers before, during or after compressing operation.

The stiffness of the rim portion may ber educed as explained in my Patent No. 2,302,178 to any desired extent by providing circumferentially spaced areas which are relatively weaker than the remainder of the diaphragm. These areas, as indicated at iii in Figure 1 may be spaced throughout the complete circumference of the rim portion and may extend from a point just within the peripheral edge of the rim to the joinder of the rim with the cone portion. The weakened areas may be uniformlyspaced or may be of either unequal spacing or unequal size in diaphragms which are non-circular such, for ex ample, as oval or generally rectangular diaphragms. The weakened portions are suchas to provide very little structural ,strength'and may be quit t n c p s so n a the arsafi cient to form a barrier to the passage of sound and air and to make the flange continuous to eliminate edge buzz.

As shown in Figures 2 and 3, the weakened portions are formed by actually reducing the thickness of the portion of the diaphragm so that the diaphragm contains less fibers in the weakened portions and issue-st t 11v. thin er than the of the o some cases the weakened portions may be so thin as to be translucent and will still function effectively. The diaphragm is supported and located by the radially extending rib portions lying between the weakened areas so that it will be accurately located and will be maintained accurately in position.

Instead of forming the weakened portions by thinning the material as shown in Figures 2 and 3, they may be formed as indicated at I4 in Figure 4 by portions of equal thickness with the remainder of the diaphragm being of less density. Areas of this type are formed by depositing less fibers on the areas l4 and by thereafter compressing the diaphragm so that its rim portion is of uniform thickness which will result in the areas I having less density and consequently less strength and rigidity than the adjacent diaphragm portions.

Figure 5 illustrates diagrammatically one form of apparatus for making diaphragms of the type shown in Figures 1 to 4 according to a spraying process. As shown, the apparatus comprises a housing which may be connected to a source of vacuum through an outlet l6 and which rotatably supports a foraminous form I! which is of substantially the same shape on its upper surface as the finished diaphragm. The form is adapted to be turned by a gear I8 meshing with teeth formed in its edge and driven by a shaft l9. Above the diaphragm and extending radially thereof is a spray manifold 2i having a plurality of spray nozzles 22 depending therefrom to discharge a suspension of fibrous material onto the form. The fibrous material may be sprayed either wet or dry as desired and may have mixed therewith an impregnating material as indicated above. One of the nozzles adjacent the periphery of the form is provided with a valve 23 which is controlled by an eccentric 2!} on the shaft 13 alternately to close and open as the shaft turns. A nozzle 24 radially beyond the nozzle carrying the valve 23 will deposit fibrous material at the edge of the form to provide an edge portion of uniform thickness.

In operation of the apparatus as the shaft I9 turns to turn the form, it will alternately open and close the valve 23 so that spaced areas around the peripheral portion of the diaphragm will receive less fibrous material than the remainder of the diaphragm. When the desired amount of fibrous material has been deposited on the form, it may be removed therefrom and subjected to a pressing or finishing operation. As the peripheral portion is pressed to a uniform thickness a structure as shown in Figure 4 will result with the portions i l of less density occurring at the points where the valve 23 was restricted to the maximum extent. Alternatively the diaphragm can be pressed to the shape shown in Figure 3 with the weakened portions 13 occurring at the points where the valve 23 was most nearly closed.

Instead of utilizing a valve in one of the nozzles, a rotating paddle 25 carried by the shaft I9 can be employed as shown in Figure 6. As the shaft l9 turns, the arms of the paddle will pass over the outlet of the endmost nozzle 22 to interrupt its discharge periodically so that less fibrous material will be deposited at circumferentially spaced points near the periphery of the form than over the remainder of the form. The extreme edge portion of the rim or flange may be made of uniform diameter by providing a nozzle 26 ofiset laterally from the nozzles 22 so thati't will not be affected by the paddle and which discharges fibrous material at the extreme peripheral edge of the form.

Figures 7 and 8 illustrate another spraying method in which the form 21 is stationary and a plurality of nozzles 28 are spaced over its upper surface to deposit fibrous material thereon. Near the periphery of the form a plurality of nozzles 29 are provided which are so spaced with respect to their elevation above the form that they will leave areas between them on which a relatively small amount of fibrous material is deposited. This operation is best seen in Figure 8 from which it will be apparent that the areas directly beneath the nozzles 29 will have fibrous material deposited thereon to a substantial depth while the areas between the nozzles will receive a much smaller amount of fibrous material to provide weakened portions in the finished diaphragm. {The remaining nozzles 28 are so spaced with respect to their elevation above the form that they will produce a uniform deposit ove the remaining area of the form. V

Figure 9 illustrates a wet method of depositing the fibrous material. The apparatus as shown in this figure comprises a vacuum chamber 3| connected to a source of vacuum through an outlet conduit 32. A foraminous generally conical form 33 is supported by the vacuum chamber with its concave side up, and the chamber is provided with an annular wall 34 extending upwardly around the periphery of the form. The space above the form within the wall 34 is adapted to be filled with an aqueous suspension of fibrous material as indicated at 35 to the level of the top of the wall 34. This provides a measured quantity of the suspension and due to theconical shape of the form produces a greater depth of suspension over the central portion of the form than over its peripheral portion. When the liquid is drawn through the form to leave the fibers deposited thereon as indicated in Figure 12, this will result in a fibrous deposit indicated at 36 which is of maximum thickness adjacent the center of the diaphragm and tapers gradually toward the diaphragm periphery. This will result in a diaphragm of maximum strength at its center portion where it is connected to the moving voice coil for maximum efiiciency and performance.

In order to produce circumferentially spaced weakened portions adjacent the diaphragm a series of spaced stop off blocks 31 are supported in the vacuum chamber on a flange 38 and closely underlie or may even actually contact the under surface of the form. These blocks will reduce the vacuum acting on the portions of the form directlyabove them thereby reducing the flow through such portions of the form. This will result in thedeposition of less fibrous material on the areas opposite the spaced blocks as shown in Figure 10 to produce weakened areas circumferentially spaced around the peripheral portion of the diaphragm. The size and spacing of the weakened portions may be controlled by the size and spacing of the blocks 31.

Instead of depositing the fibrous material from a wet solution, the same effect can be obtained with a dry suspension as illustrated in Figure 11. In this figure a vacuum chamber 4! is connected to a source of vacuum through a conduit 42 and carries an inverted conical foraminous form l3. The vacuum chamber carries above the of the form' may be periodically restricted by blocking members 46 carried by a flange 41.

In practicing the method with this apparatus, a measured quantity of dry fibrous material suspended in air may be injected into the chamber 44 and uniformly distributed through the entire chamber. Vacuum in the vacuum chamber will draw the suspended fibrous material on to the form, and since the suspension is of greater depth over the central part of the form than at its periphery, the deposited material will be tapered in thickness as shown at 36 in Figure 12. The blocks 46 will reduce the vacuum at spaced points ad- 'jacent the periphery of the diaphragm to produce weakened portions.

Figure 13 illustrates an alternative form of diaphragm which may be made by the method of the present invention and which includes a generally conical body portion 48 terminating in a circumferentially corrugated flange 49. The flange 49 connects to an axially extending portion 5| which in turn connects to a radially extending rim 52. The flange is preferably formed with spaced weakened areas 53 which extend over the corrugated portion 49 and along the axial portion 5| approximately to the juncture thereof with the rims 52.

This construction can be formed according to any of the several alternative method steps described above either by properly shaping the form during the final pressing operation or by a "combination of both. In the completed diaphragm the axial flange portion increases the flexibility of support of the diaphragm body.

It will be understood that the deposited fibrous material after deposition on the form by any of the methods described above may be stripped from the form and pressed to the desired finished shape and density. The forms employed may correspond exactly with the desired finished shape or may only roughly correspond with the desired shape and may be brought to the desired shape during the pressing operation.

While several methods for carrying out my invention have been specifically described herein, it will be understood that they are illustrative only and are not to be taken as a definition of the scope of the invention, reference being had for this purpose to the appended claims.

What is claimed is:

1. In a method of making acoustic diaphragms, the steps of depositing fibrous material upon a form to produce a diaphragm having a body portion and a peripheral supporting portion, and during said deposition reducing the quantity of fibrous material deposited on circumferentially spaced areas disposed near the peripheral edge of the diaphragm whereby such spaced areas will be weaker than the remainder of the peripheral edge portion of the diaphragm.

2. In a method of making acoustic diaphragms, the steps of depositing upon a form having a generally conical body portion and a peripheral flange portion fibrous material in an opaque continuous layer, to cover the body portion and circumferentially spaced radially extending portions only of the flange, depositing a thinner translucent and porous layer of fibrous material on the flange portion between the spaced radially extending portions, and thereafter impregnating the flange with a filling and impregnating materialto make the last mentioned deposited portions non-porous.

3. In a method of making acoustic diaphragms, the steps of depositing fibrous material upon a form to produce a diaphragm having a body portion and a peripheral supporting portion, and masking circumferentially spaced areas disposed near the peripheral edge of the diaphragm during the deposition so that lesser amounts of fibrous material will be deposited on said areas than on the remainder of the diaphragm.

4. The method of claim 1 wherein the fibrous material is compressed after depostion to a uniform thickness throughout its peripheral portion so that said spaced areas will be of the same thickness as but of less density than the remainder of the peripheral portion.

5. In a method of making acoustic diaphragms, the steps of rotating a circular form,

spraying fibrous material on the form from fixed positions as the form rotates, and periodically reducing the quantity of fibrous material sprayed on the form from one of said fixed positions adjacent to the periphery of the form to cause less fibrous material to be sprayed on circumferentially spaced areas adjacent to the periphery of the form than on the peripheral portion of the form between said areas to produce circumferentially spaced areas adjacent to the periphery of the form containing less fibrous material than adjacent areas.

6. The method of making acoustic diaphragms which includes the steps of suspending fibrous material above a porous form having the general configuration of a diaphragm with a generally conical body portion and a peripheral flange, subjecting the lower side of the form to vacuum to cause the suspended fibrous material to deposit on the form, and partially masking circumferentially spaced areas disposed near the peripheral edge of the form during the deposition so that lesser amounts of fibrous material will be deposited on said areas than on adjacent areas of the form.

JOSEPH B. BRENNAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 523,113 Fairbanks July 1'7, 1894 709,228 Kron Sept. 16, 1902 1,165,677 King Dec. 28, 1915 1,415,649 Jagenburg May 9, 1923 1,616,222 Harrigan Feb. 1, 1927 1,701,238 Kennedy Feb. 5, 1929 1,819,300 Newcombe Aug. 18, 1931 1,848,055 Chaplin Mar. 1, 1932 1,872,081 Hawley Aug. 16, 1932 1,872,583 Hawley Aug. 16, 1932 1,952,168 Hawley Mar. 27, 1934 1,952,169 Hawley Mar. 27, 1934 1,984,018 Hawley Dec. 11, 1934 1,984,019 Hawley Dec. 11, 1934 1,995,904 Sherman Mar. 26, 1935 2,079,667 Swift May 11, 1937 2,081,740 Farnham May 25, 1937 2,159,638 Schur May 23, 1939 2,302,178 Brennan Nov. 17, 1942 2,348,725 Chaplin May 16, 1944 2,411,066 Stevens Nov. 12, 1946 FOREIGN PATENTS Number Country Date 101,218 Australia Oct. 28, 1937 

